Cable modem tuner

Abstract

An IF signal output from an IF amplifying circuit included in a tuner is converted to have a band width for transmission by an SAW filter and has unnecessary signals removed therefrom. Thereafter, the resulting signal has its gain made constant by an IFAGC circuit, amplified by an IF amplifying circuit, unnecessary band components are removed by a lowpass filter, and balanced IF signals are output from unbalance/balance converting circuit and provided to a QAM demodulating circuit.

1. A cable modem tuner, comprising:
 a tuner portion taking and amplifying a signal corresponding to a reception channel from input signals, and converting to an intermediate frequency signal; 
 a surface acoustic wave filter connected to an output of said tuner portion and limiting said intermediate frequency signal to a frequency band for transmission; 
 a gain control unit connected to an output of said surface acoustic wave filter, including at least one dual gate type MOSFET and performing control based on an externally provided control voltage such that gain of said intermediate frequency signal is constant; 
 an intermediate frequency amplifying unit connected to an output of said gain control unit and amplifying said intermediate frequency signal; 
 a lowpass filter connected to an output of said intermediate frequency amplifying unit and limiting the output of said intermediate frequency amplifying unit by filtering out a signal out of a transmission band; and 
 an unbalance/balance converting circuit connected to an output of said lowpass filter and converting an unbalanced signal into a balanced signal to output the balanced signal to a QAM demodulating circuit.